Device for measuring stress in a tie bolt



March 29, 1966 G. w. CARRIE DEVICE FOR MEASURING STRESS IN A TIE BOLT Filed Dec. 6, 1965 F/G. 3 if United States Patent Ofilice 3,242,725 Patented Mar. 29, 1966 3,242,725 DEVICE FOR MEASURING STRESS IN A TIE BOLT George W. Carrie, Marlborough, Conn., assignor to United Aircraft Corporation, East Hartford, Conn., a corporation of Delaware Filed Dec. 6, 1963, Ser. No. 328,573 7 Claims. (Cl. 7388) This invention relates to a device for measuring the stress applied to a tie bolt or tie rod for use, for example, in holding together a plurality of rotor discs in an axial flow compressor or turbine One feature of the invention is an arrangement for measuring the elongation of the rod or bolt to determine the stress applied thereto, thereby to establish the clamping pressure applied by the bolt or series of bolts to the parts clamped thereby. Another feature is an apparatus which can function to measure the bolt elongation without in any way reducing the strength of the tie bolt.

One feature of the invention is a tie rod so constructed that the elongation of the rod may be measured after the rod is stressed with a provision for insertion and removal of the measuring device without affecting the tie rod and without varying the stress applied thereto.

Other features and advantages will be apparent from the specification and claims, and from the accompanying drawing which illustrates an embodiment of the invention.

FIG. 1 is a fragmentary sectional view through a turbine showing the tie bolt applied thereto.

FIG. 2 is a perspective view of the tie bolt with the measuring device associated therewith.

FIG. 3 is a sectional view through the tie bolt.

The invention is shown for use in determining the stress applied to a tie belt which is one of several used in holding two spaced discs of a turbine rotor in assembled relation. Referring first to FIG. 1, the turbine, which may be similar to that shown in the Batt Patent No. 2,680,001, has spaced rows of turbine vanes 2 and 4 and similarly spaced rows of turbine blades 6 and 8 downstream respectively of the two rows of vanes. The blades 6 and 8 are carried on rotor discs 10 and 12 which are held in spaced relation to each other by a ring of sleeves 14 circumferentially spaced apart and extending between the discs. The discs 10 and 12, the spacer sleeves 14 and end hubs 16 and 18 which support the discs in the turbine are held in assembled relation by a plurality of tie bolts 20 or tie rods which are arranged in a ring concentric to the axis of the discs and extend through aligned openings in the respective hubs and discs and through the spacer sleeves 14. Each tie bolt 20 has a nut 22 at one end engaging a threaded portion 24 at this end of the tie bolt, this threaded portion being small enough to permit insertion of the bolt through the openings in the hubs and discs. The bolt 20 also has spaced ribs 26 thereon in a position to engage with the openings in the hubs and discs and with the sleeves and thereby to center the discs, hubs and sleeves with respect to each other. Thus, one of the ribs 26 pilots both the end hub 16 and the disc 10 and the next adjacent rib 26 pilots both the disc 10 and the adjacent end of the sleeve 14. Other ribs are similarly located to pilot both the disc and the sleeve or hub adjacent thereto. At the end of the tie bolt remote from the threaded portion 24 is another enlarged diameter rib 28 which is threaded at 30 to receive a clamping nut 32. The rib 28 is larger in diameter than the ribs 26, as will be apparent. If desired, beyond the rib 28 on the bolt may be another rib or head 34 which is knurled as at 36 so that the bolt may be prevented from turning while the clamping nut 32 is being tightened against the end hub 18.

For the purpose of measuring the elongation of the tie bolt, each of the several ribs 26 has a groove 38 therein with the grooves in the several ribs in alignment with each other and in alignment with an axially extending passage 40 in the rib 28 and a passage 42 in the rib 34. The measuring device consists of an indicator 44 having a projecting rod 46 to actuate the indicator and a sleeve 48 surrounding the rod at the end adjacent to the indicator and fixed to the base 50 of the indicator. Movement of the free end of the rod 46 with respect to the end of the sleeve 48 indicates the change in dimension on the indicator. The endmost rib 26 adjacent to the threaded end 24 of the bolt has an axial stop 52 for engagement with the end of the rod 46 when this rod is inserted through the passages 40 and 42 and grooves 38 in the bolt.

In use, the bolt is assembled with the discs and hubs into the position shown, the nut 22 having been removed until the bolt is in position. The nuts 22 and 32 are then set up to hold the device in position. Prior to tightening of the nuts, the measuring device is used to determine the exact distance from the stop 52 to the end of the bolt adjacent to the rib 34. The nut 32 is then tightened, the bolt being held against turning by a suitable wrench engaging with the knurled rib 34. When the nut 32 has been tightened approximately to the proper tension, the measuring device is inserted in position in the passages in the ribs and the amount that the bolt is elongated by tightening of the nut 32 is determined.

The elongation of the bolt is directly related to the stress applied to the bolt as will be apparent and, by computation, it is easily determined what the bolt elongation should be in order to apply the necessary clamping action to the rotor assembly. Thus, by accurate measurement of the bolt elongation, the exact stress on the bolt may be determined. When the desired elongation is obtained, the measuring device may be withdrawn from the grooves and passages in which it is positioned. It will be apparent that the grooves are located entirely in the ribs on the bolt and thus external of the elfective load carrying portion of the bolt so that the presence of the grooves does not affect in any way the strength of the bolt and does not create any detrimental local stress therein.

It is to be understood that the invention is not limited to the specific embodiment herein illustrated and described, but may be used in other ways without departure from its spirit as defined by the following claims.

I claim:

1. A tie bolt for use in the assemblage of a plurality of disc-like elements in axial alignment, said bolt having a threaded rib adjacent one end, and a nut on said rib for applying and axial load to the bolt, said bolt also having a plurality of axially spaced ribs thereon, in combination with a measuring rod, aligned axial grooves in said spaced ribs through which the measuring rod is inserted, the groove in the end spaced rib remote from the nut having an axial stop therein to engage the end of the rod, and said threaded rib being larger in diameter than the spaced ribs and having a bore therein radially inward of the threads in alignment with the grooves in the spaced ribs to receive the measuring rod without interfering with turning of the nut on the threaded rib.

2. A tie bolt assembly for applying a predetermined load to articles clamped thereby including a bolt having threads at one end, a clamping nut on said threads, a plurality of axially spaced ribs :on said bolt, an axial groove in each of said ribs, said grooves being in axial alignment, a threaded end rib on said bolt adjacent the other end, and a clamping nut engaging said threaded rib, the latter rib having an axial passage therein in alignment with said grooves, in combination with a measuring device having a projecting stem for positioning in said axial passage and said grooves and a base engaging with said other end of the tie bolt for measuring the elongation of the bolt resultting from tightening the clamping nuts.

3. A tie bolt as in claim 2 in which the ribs on the bolt are large enough in diameter to receive the full dimension of the groove, the latter grooves and the axial passage being larger than the projecting stern of the measuring device.

4. A tie bolt as in claim 2 in which the rib adjacent said one end of the rod has an axial stop therein for engagement by the end of the projecting stem.

5. In a rotor assembly, a plurality of spaced axially aligned discs, a plurality of axial passages through said discs, and tie rods extending through said passages, each rod having ribs thereon for engagement with the discs, spacers adjacent the rods to hold the discs in spaced relation and clamping nuts on the rod ends for engaging the end discs, one clamping nut being located on a threaded rib on the bolt and means for measuring the elongation of each tie bolt when the clamping nuts are tightened, including aligned grooves in said ribs and an aligned passage in said threaded rib, a stem on said measuring means extending through said passage and lying in said grooves,

the endmost groove remote from the threaded rib having an axial stop in said groove to locate the end of the stem, and a stop ring carried by said measuring means for engagement with the end of the bolt adjacent the threaded rib, the measuring means determining the elongation of the bolt from the end adjacent the threaded rib to the axial stop.

6. An assembly as in claim 5 in which the aligned grooves and passage are larger in dimension than the stem of the measuring means.

7. An assembly as in claim 5 in which the grooves in the ribs and the axial passage are located entirely outside the eifective load carrying portion of the bolt.

RICHARD C. QUEISSER, Primary Examiner.

C. A. RUEHL, Assistant Examiner. 

1. A TIE BOLT USE IN THE ASSEMBLAGE OF A PLURALITY OF DISC-LIKE ELEMENTS IN AXIAL ALIGNMENT, SAID BOLT HAVING A THREADED RIB ADJACENT ONE END, AND A NUT ON SAID RIB FOR APPLYING AND AXIAL LOAD TO THE BOLT, SAID BOLT ALSO HAVING A PLURALITY OF AXIALLY SPACED RIBS THEREON, IN COMBINATION WITH A MEASURING ROD, ALIGNED AXIAL GROOVES IN SAID SPACED RIBS THROUGH WHICH THE MEASURING ROD IS INSERTED, THE GROOVE IN THE END SPACED RIB REMOTE FROM THE NUT HAVING AN AXIAL STOP THEREIN TO ENGAGE THE END OF THE ROD, AND SAID THREADED RIB BEING LARGER IN DIAMETER THAN THE SPACED RIBS AND HAVING A BORE THEREIN RADIALLY INWARD OF THE THREADS IN ALIGNMENT WITH THE GROOVES IN THE SPACED TO RECEIVE THE MEASURING ROD WITHOUT INTERFERING WITH TURNING OF THE NUT ON THE THREADED RIB. 